Synthesis and characterization of new thermosetting polybenzoxazines with other functional groups in the network

In this work, novel thermosetting systems of high performance based on multi-functional benzoxazines were developed. First, 3-(2-hydroxyethyl)-3,4-dihydro-2H-1,3-benzoxazine (BzOH) and bis(3-(2-hydroxyethyl)-3,4-dihydro-2H-1,3- benzoxazinyl) isopropane (BzPOH) monomers were synthesized by reaction between phenol or bisphenol A, paraformaldehyde, and ethanolamine. Then, BzOH and BzPOH were functionalized with maleic anhydride using a stoichiometric ratio of oxazine: maleic anhydride (1:1) to produce low molar mass species with carboxylic acid groups, named BzFA and BzPFA. The products were characterized by Nuclear Magnetic Resonance (NMR), Size-Exclusion Chromatography (SEC), and Fourier Transform Infrared Spectroscopy (FTIR). BzFA and BzPFA exhibited weight-average molecular weights of 5000 g.mol⁻¹and 50,000 g.mol⁻¹, respectively. Mixtures between the new precursors and the conventional benzoxazine (BzBA) derived from bisphenol A and aniline [bis(3-phenyl-3,4-dihydro-2H-1,3benzoxazinyl) isopropane] were prepared. The curing process was studied by FTIR and Differential Scanning Calorimetry (DSC), and viscoelastic, mechanical, thermal, and morphological properties of the materials were also evaluated. Materials obtained exhibited better thermal, viscoelastic and mechanical properties than conventional polybenzoxazine. Scanning Electron Microscope (SEM) measurements indicated homogeneous material surfaces.